Automated catalyst regeneration in a reactor

ABSTRACT

A technique, including an apparatus, for automatically regenerating a catalyst used in a process for obtaining a product in an exit stream from a raw material in a feed stream of a reactor, comprises determining the concentration of raw material in the feed and exit stream and obtaining a value for the catalyst selectively as a function of the difference between the concentrations. When a selected selectivity is reached, which is indicative of the need for the catalyst to be regenerated, regenerator equipment is activated for regenerating the catalyst in the reactor. To continue the process, the feed stream is transferred to an auxiliary reactor during regeneration of the primary reactor, which contains regenerated or fresh catalyst. When used in reactors for the hydrogenation of acetylene to ethylene, the concentration of hydrogen in the feed stream is also calculated with the selectivity equaling the concentration of hydrogen divided by the difference in concentrations for the acetylene in the feed and exit streams respectively.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates in general to catalyst reactors and inparticular to a new and useful method and apparatus of automaticallyregenerating a catalyst.

In many chemical, petrochemical and synthetic fuel manufacturingprocesses a raw material feed stream is passed over a catalyst in areactor to either produce a desired product or remove certainimpurities. The state of the catalyst is of prime importance to theseoperations because economic operation of a reactor and consequently theplant, is very much affected by the catalyst state. Product conversion,yield and operating temperature are dependent upon the selectivity ofthe catalyst.

A catalyst's selectivity decays with time because of a number of factorssuch as presence of impurities and their concentration in the feedstream, types of byproducts from side reactions, duration of reactoroperation, etc. For example in the selective hydrogenation of acetylenein an ethylene rich stream green oil, polymerization of green oil on thecatalyst surface, etc. occurrs. These are deposited on the catalystsurface, thus reducing the surface area available for the reaction.Hence, acetylene hydrogenation to ethylene is reduced. The condition mayalso lead to a product which is off specification. Therefore, afteroperating a reactor with fresh or regenerated catalyst for some time,the catalyst is either regenerated by passing steam through the reactoror replaced by new catalyst whichever may be the case depending on aspecific situation.

The state of the art for control of the selective hydrogenation ofacetylene into ethylene in the ethylene rich stream is well documentedin the following patents:

    ______________________________________                                        1.     U.S. Pat. No.                                                                            2,802,889   Frevel et al                                    2.     U.S. Pat. No.                                                                            2,814,653   Hogan et al                                     3.     U S. Pat. No.                                                                            3,113,980   Robinson et al                                  4.     U.S. Pat. No.                                                                            3,153,679   Rottmayr                                        5.     U.S. Pat. No.                                                                            3,471,582   Lupfer                                          6.     U.S. Pat. No.                                                                            3,656,911   Hobbs                                           7.     U.S. Pat. No.                                                                            3,972,804   McLaughlin et al                                8.     U.S. Pat. No.                                                                            4,236,219   Killebrew et al                                 9.     U.S. Pat. No.                                                                            4,241,230   Drinkard                                        10.    U.S Pat. No.                                                                             4,249,907   Callejas                                        ______________________________________                                    

These patents only teach the techniques for the temperature control ofreactors. They do not provide for any indication of the current state ofthe catalyst. Consequently, any or all of the following situations mayoccur:

1. As catalyst selectivity decreases, less and less acetylene will behydrogenated into ethylene. Thus, the probability for occurrence ofproduct off-specification increases and ultimately may occur, thusresulting in loss of production.

2. The operator may increase operating temperature of the reactor tocompensate for decline in catalyst selectivity on the basis ofinformation from the manufacturer of the catalyst and acetyleneconcentration in the reactor exit stream. This presents a situationwhere an operator may be unable to discriminate among the causes foroccurrences of more than normal acetylene concentration in the exitstream. This may be a result of several possible conditions, forexample, sudden drop in feed temperature, sudden breakthrough ofacetylene in cracking furnaces, malfunctioning of intermediate unitoperations or their associated components, malfunctioning/failure ofinstruments, etc.

3. Increase in operating temperature of the reactor results inincreasing energy consumption in the feed preheater, thus increasingcoolant use in the inter catalyst bed cooler, and increases ethylenehydrogenation to ethane.

Moreover, in the current state of the art industrial practice, catalystis regenerated either after occurrence of a severe product offspecification or it has been scheduled by maintenance personnel on thereactor, on the basis of an elapsed period of operation or during plantshutdown. The same is applicable to catalyst change. Therefore, thereactor is normally operated with catalyst for a period longer than therecommended period between two successive regenerations and replacementby fresh catalyst. Therefore, one or more of the aforementioned threeconditions may occur, or worse yet, the catalyst may be poisoned. Therecommended period of operation between two successive catalystregeneration is about 18 months. Continued operation withoutregeneration may poison the catalyst completly, thus reducing its life(normally about 5 years) and may require new catalyst.

SUMMARY OF THE INVENTION

The present invention is drawn to a method and apparatus for theautomatic regeneration of catalyst in a reactor which is based on avalue of the catalyst selectivity.

According to the invention, catalyst is regenerated in a timely fashion.This is important in view of the high cost of catalyst and thepossibility of poisoning the catalyst beyond the point where it can beregenerated.

The invention also relates to an apparatus and method for the automaticregeneration of catalyst in a reactor wherein selective hydrogenation ofspecific unsaturated hydrocarbon is conducted for its removal from anolefin rich stream.

According to another feature of the invention, a standby reactor isavailable for the automatic regeneration of catalyst in a primaryreactor. The invention can operate regardless of the type of reactor orcatalyst except for the fluidized bed type of reactor.

Accordingly, an object of the present invention is to provide anapparatus for the automatic regeneration of catalyst used in a processfor obtaining a product in an exit stream of a reactor, from a rawmaterial in a feed stream of the reactor, the reactor havingregeneration means activatable to regenerate the catalyst, comprising,first sensor means operatively connected to the feed stream for sensinga concentration of raw material in the feed stream, second sensor meansoperatively connected to the exit stream for sensing a concentration ofraw material in the exit stream and a control system connected to thefirst and second sensor means for calculating a value for selectivity ofthe catalyst as a function of raw material concentration in the feed andexit streams, and for generating a control signal when the calculatedselectivity value approaches a selected selectivity value whichindicates the catalyst should be regenerated, the control systemconnected to the regeneration means for activating the regenerationmeans to regenerate the catalyst.

A further object of the invention is to provide such an apparatus whichincludes an auxiliary reactor having fresh or regenerated catalyst usedin the process, the auxiliary reactor connected to the feed and exitstreams over valves which are connected to and controlled by the controlsystem to transfer the feed stream to the auxiliary reactor when thefirst mentioned reactor is undergoing regeneration of its catalyst.

A still further object of the invention is to provide such an apparatuswherein the process is the selective hydrogenation of a specificunsaturated hydrocarbon forming the raw material, for its removal froman olefin rich stream, the first and second sensor means operable tosense a concentration of the hydrocarbon in the feed and exit streamsrespectively with the first sensor means also being operable to sense aconcentration of hydrogen in the feed stream, the control systemincluding calculator means for calculating the selectivity of thecatalyst according to the relationship C_(H1) /(C_(A1) -C_(A2)), whereinC_(H1) is the concentration of hydrogen in the feed stream, C_(A1) isthe concentration of hydrocarbon in the feed stream and C_(A2) is theconcentration of hydrocarbon in the exit stream.

Another object of the invention is to provide a method of regeneratingcatalyst in a process for obtaining a product in an exit stream from araw material in a feed stream, comprising sensing the concentration ofraw material in the feed stream, sensing the concentration of rawmaterial in the exit stream and determining the selectivity of thecatalyst for the specific process as a function of the differencebetween the feed stream concentration and the exit stream concentrationfor the raw material.

Another object of the invention is to provide a method of regenerating acatalyst comprising providing an auxiliary reactor connected in parallelto a main reactor, to which the process is transferred duringregeneration of catalyst in the primary reactor.

Another object of the invention is to provide a method of regeneratingcatalyst in an automatic manner using a NETWORK 90 system available fromthe Bailey Meter Company.

Another object of the invention is to provide an apparatus forautomatically regenerating catalyst which is simple in design, rugged inconstruction and economical to manufacture.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic representation of an automatic catalystregeneration system showing dual reactors with control and sensingelements;

FIG. 2 is a block diagram showing additional details of a centralcomputer system used in accordance with the invention;

FIG. 3 is a block diagram showing additional details of a unit found inthe control computer for establishing an actual catalyst selectivityvalue;

FIG. 4 is a block diagram showing additional details of a unit in thesub-computer for determining whether the actual selectivity calculatedhas reached a selected limit for the selectivity;

FIG. 5 is a block diagram showing a series of three sub units in thecontrol computer which control the operation of the overall apparatus totransfer operation from one of the reactors to the other reactor andthereafter regenerate the catalyst of the first reactor; and

FIG. 6 is a block diagram showing additional details of units in thecontrol computer for monitoring catalyst status and for setting varioustime durations used in controlling the apparatus using the controlelements of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in particular, the invention embodied therein,in FIG. 1, comprises an apparatus for automatically regenerating acatalyst in one of two reactors 10 and 110 which are of substantiallyidentical design.

The reactor 10 is used as a primary reactor in a process for obtaining aproduct from a raw material using a catalyst, with the other reactor 110being utilized as an auxiliary reactor during the period when thecatalyst in the primary reactor is being regenerated.

The specific example illustrated involves a process for the selectivehydrogenation of acetylene to ethylene. The invention is suitablehowever, in the regeneration of catalysts in other processes.

As shown in FIG. 1, the feed stream containing ethylene, acetylene andhydrogen is provided over a feed line 2, past a heater 4 which, forexample, uses steam and to inlet valve 12 at the inlet of primaryreactor 10. Since the reactors 10 and 110 are substantially identical,corresponding parts in the two reactor systems will be designated withthe same numerals except that numerals associated with the auxiliaryreactor 110 are increased by 100.

A steam line 6 is connected to the inlet of reactor 10 and includes aregenerator valve 8. Line 6 is connected to a steam source 90 over amain steam valve 92 controlled by a FIC controller 94 which reacts to acomputer control signal as well as a flow transmitter 96. With valves 8and 92 open, steam is provided to the catalyst in reactor 10, toregenerate the catalyst.

In normal operation of reactor 10 for producing acetylene, however, atleast valve 8 is closed. A line connects the outlet of reactor 10 to anoutlet valve 14. A drain valve 16 is connected to a drain line upstreamof outlet valve 14 for draining waste products of the regenerationcycle.

An exit line 98 is connected to the outlet valve 14 of reactor 10 aswell as the outlet valve 114 of reactor 110.

Each of the reactors consists of two reactor beds separated by anintermediate cooling bed. The cooling bed of reactor 10 is connected toa cooling circuit 18 having a bypass valve 20 for regulating thetemperature in reactor 10. Coolant is supplied to a heat exchanger 24over a coolant valve 22. An identical cooling circuit 118 is providedfor auxiliary reactor 110.

A chromatograph 91 measures the concentration of acetylene and hydrogenin the feed stream of feed line 2 and a second chromatograph 93 measuresthe concentration of acetylene in the exit stream of exit line 98.

Chromatographs 91 and 93 may be replaced by any suitable sensor forsensing raw material concentration in the feed and exit lines.

All sensors are connected to the computer system over analog to digitalconverters 52. The steam valve controller 94 is connected over a digitalanalog converter 54, to computer system 50.

The instrumentation and control schemes for reactors 10 and 110 areutilized for modulating the systems, as well as startup and shutdownoperations. Specific details on the operation of the separate systems isknown in the art and demonstrated in the above-identified patents.

In accordance with the invention, primary reactor 10 is initially usedfor the selective hydrogenation process while reactor 110 containsregenerated or fresh catalyst that is available for subsequent use.

In this state of the apparatus, valves 12, 22 and 14 are open whilevalves 8 and 16 are closed. All of the corresponding valves, 108, 112,114, 116, and 122, in the auxiliary reactor system, are closed. Valve 20is active for temperature control purposes in the selectivehydrogenation process. While valve 120 is inactive. Valve 92 is closedsince it is used for modulating control during the regeneration process.

As will become apparent hereinunder, the key features of the inventivecontrol structure and method are:

1. The estimation of catalyst selectivity;

2. The detection of catalyst selectivity below a normal required level;

3. Transfer of selective hydrogenation to the auxiliary reactor 110 upondetection of an unsatisfactory condition in the catalyst of primaryreactor 10;

4. The subsequent regneration of catalyst in reactor 10;

5. The bringing of primary reactor 10 to a ready state for the takeoverof selective hydrogenation from reactor 110; and

6. Catalyst status accounting.

In accordance with the invention, a measurement of catalyst selectivitytoward acetylene hydrogenation to ethylene is obtained by the algorithm:

    S=C.sub.H1 /(C.sub.A1 -C.sub.A2)

where;

S=Selectivity of the catalyst

C_(A1) =Acetylene concentration in the feed stream

C_(A2) =Acetylene concentration in the exit stream

C_(H1) =Hydrogen concentration in the feed stream.

Acetylene and hydrogen concentration in the feed stream are provided bychromatograph 91. Acetylene concentration in the exit stream is providedby chromatograph 93. These signals are provided to the control computersystem 50 where they are processed for noise and converted toengineering units in a signal processing block 26 shown in FIG. 2. Thisis based on known principles of signal processing.

The signals are then provided to selectivity calculation block 28 wherethe selectivity calculation is performed according to the algorithm setforth above. Details of block 28 are shown in FIG. 3 where a subtractionunit 30 takes the difference between feed and exit stream acetyleneconcentrations which value forms the divisor of the hydrogenconcentration in a division unit 32. The output of unit 32 is sent to adisplay block 34 as well as a desired selectivity block 36.

The current selectivity value for the catalyst is thus displayed to theoperator over display block 34 which is of known design.

Details of block 36 for determining whether the catalyst selectivity hasfallen to a set limit, are shown in FIG. 4. This value Z is set in limitunit 38 and is based on manufacturers recommendation and operatingexperience with the particular catalyst being used.

If the actual selectivity is still above this limit, a signal issupplied over a form message unit 39 to a catalyst status accountingblock 40. When actual selectivity has fallen to the limit, a signal issent to a transfer block 42 for initiating transfer of the process fromthe primary to the auxiliary reactor.

FIG. 5 shows details of the transfer block 42 as well as catalystregeneration block 44 and ready state block 46.

As shown in FIG. 5, the valves in the apparatus of FIG. 1 are controlledin appropriate sequence and with time delays where necessary.

Valve 122 is first opened to supply coolant to heat exchanger 124 incooling circuit 118 of auxiliary reactor 110. Valve 112 is then openedto establish a flow of raw materials from feed line 2 to reactor 110. Aduration of T1 seconds is then observed to fill reactor 110 onappropriate level, whereafter outlet valve 114 is opened forestablishing flow of products to exit line 98. Inlet valve 12 of reactor10 is then closed and a second time period of T2 seconds is observed.After this time period which permits drainage of primary reactor 10,outlet valve 14 is closed. After this coolant valve 22 is closed and amessage is provided to display 34 for the purpose of informing theoperator that the initial transfer steps have been taken.

A waiting period of T3 minutes is then observed after which regenerationfor primary reactor 10 is commenced. To achieve these control functions,block 44 first opens drain valve 16. Regeneration valve 8 is then openedto commence the regeneration of catalyst in reactor 10. The remainder ofsteps illustrated in block 44 of FIG. 5 complete the regenerationprocess in known fashion using the controller 94 and flow transmitter 96further in conjunction with appropriate programming in control computersystem 50.

With regeneration complete, a message signal is again provided todisplay 34, for operator information. Regeneration valve 8 is thenclosed by appropriate controls in ready state block 46. After observingan appropriate duration of time T7 for drainage of reactor 10, drainvalve 16 is closed and a further message is sent to display 34 whichindicates that the primary reactor 10 is now again available for furtheruse. A last step in the automatic regeneration system of the inventionis an accounting for the total time between two successiveregenerations, the total time for use of catalyst and the total numberof regenerations This is accomplished in control block 40 which is shownin greater detail in FIG. 6.

The circuit of FIG. 6 permits the operator to manually initiate aregeneration step over a block 56. Regeneration also is begun whenevertotal time between successive regenerations is greater than a specifiedtime TOTALT. Regeneration may also be initiated when total time forusage exceeds a total specified time STIME. The number of regenerationsNGEGEN is also counted in the circuitry of FIG. 6 with a new catalystbeing provided after a selected number of regeneration cycles SREGEN.

The various messages which are provided to the operator by the variousblocks are as follows:

1. Reactor 10 to be switched to reactor 110 automatically;

2. Reactor switchover complete;

3. Catalyst regeneration process started;

4. Catalyst being regenerated in reactor;

5. Catalyst regeneration complete;

6. Reactor being switched because of

(a) selectivity below acceptable level or;

(b) operator demand or;

(c) operating duration at selected limit; and

7. New catalyst required.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. An apparatus for the automatic regeneration ofcatalyst used in a process for obtaining ethylene in an exit stream of areactor from acetylene in a feed stream of the reactor, the reactorhaving regeneration means for regenerating the catalyst,comprising;first sensor means including a chromatograph operativelyconnected to the feed stream for sensing a concentration of acetyleneand hydrogen in the feed stream; second sensing means including achromatograph operatively connected to the exit stream for sensing aconcentration of acetylene in the exit stream; a control systemconnected to said first and second sensor means and to the regenerationmeans of the reactor for calculating a value for selectivity of thecatalyst according to the relationship:

    S=C.sub.H1 /(C.sub.A1 -C.sub.A2),

wherein C_(H1) is the hydrogen concentration in the feed stream, C_(A1)is the acetylene concentration in the feed stream and C_(A2) is theacetylene concentration in the exit stream, and for generating a controlsignal when the calculated value for the selectivity approaches aselected value for the selectivity which selected value is indicativethat the catalyst should be regenerated, said control signal beingapplied to the regeneration means for activating the regeneration meansto regenerate the catalyst; and an auxiliary reactor containing catalystfor the process connected to the exit stream and the feed stream, valvemeans operatively engaged in at least one of the exit and feed streams,connected to said control system for supplying acetylene to saidauxiliary reactor when the regeneration means are activated toregenerate catalyst in the first mentioned reactor.
 2. An apparatusaccording to claim 1, including desired selectivity means for receivingsaid selected selectivity value and connected to said control system,said desired selectivity means operable to generate said control signalwhen said calculated selectivity value approaches selected selectivityvalue.
 3. An apparatus according to claim 2, including catalyst statusaccounting means connected to said desired selectivity means forreceiving a signal from said desired selectivity means when saidcalculated selectivity value has not approached said selectedselectivity value, said catalyst status accounting means operable todetermine a time period during which the process is conducted with thecatalyst before it is regenerated.
 4. An apparatus according to claim 3,wherein said catalyst status accounting means is connected to thecatalyst regeneration means, said catalyst status accounting meanshaving desired time period setting means operable to compare a desiredtime period for use of the catalyst with the actual time period duringwhich the catalyst has been used and, when the actual time periodreaches the desired time period, activating the regeneration means. 5.An apparatus according to claim 3, wherein said catalyst statusaccounting means includes regeneration counting means for counting thenumber of times the catalyst in the reactor has been regenerated,display means connected to said catalyst status accounting means fordisplaying a message when the number of times the catalyst has beengenerated reaches a selected number of times for catalyst regeneration.6. An apparatus for a catalytic reaction with automatic catalystregeneration comprising;a first reactor with an input and an output andat least one catalyst bed; a second reactor having an input and anoutput and at least one catalyst bed, said reactors being for thehydrogenation of a hydrocarbon; a feed line connected to the input ofsaid first and second reactors; an exit line connected to the output ofsaid first and second reactors; an input valve connected in the input ofeach reactor; a regeneration line connected to the input of eachreactor, regeneration means connected to said regeneration line forregenerating catalyst in each reactor, a regeneration valve connectedbetween the input of each reactor and said regeneration means; a firstsensor connected to the feed line for sensing the concentration of a rawmaterial to be reacted in at least one of said reactors with the aid ofsaid catalyst to convert the raw material into a product; a secondsensor in said exit line for sensing the concentration of raw materialin the exit line, said first and second sensors operable to measure aconcentration of hydrocarbon and acetylene in said feed line andacetylene in said exit line; a control system connected to said firstand second sensors, said inlet valves and said regenerator valves, saidcontrol system including means for calculating an estimated catalystselectivity according to the algorithm:

    S=C.sub.H1 /(C.sub.A1 -C.sub.A2),

wherein S=catalyst selectivity, C_(H1) is the hydrogen concentration inthe feed stream, C_(A1) is the acetylene concentration in the feedstream, and C_(A2) is the acetylene concentration in the exit stream,and comparing the estimated catalyst selectivity to a set limit forcatalyst selectivity, said control system operable to maintain theprocess in one of said reactors by maintaining the inlet valve of saidone of said reactors open, and for transferring the process to the otherreactor by opening the inlet valve of the other reactor and closing theinlet valve of the one of said reactors, said control system furtheroperable to activate said regeneration means and open said regenerationvalve of said one of said reactors while maintaining the regeneration ofthe other of said reactors closed; counting means for counting thenumber of regenerations and comparing that count to a predeterminednumber; and indicating means to provide a signal indicative of arequirement for new catalyst when said number of regenerations exceedssaid predetermined number.